Gabriel E. Gomez, the Republican nominee for the US Senate special election, reported adjusted gross income of $10.1 million over six years as a private equity investor, accord­ing to tax returns made available by his campaign on Wednesday.

Gomez paid $2.1 million in taxes during that same period, from 2006 through 2011, his filings show. His average effective tax rate of 21 percent over that period reflects the tax benefits in private equity, where investment profits are taxed at a lower rate than other ­income.

A former US Navy SEAL who turned to private equity investing after graduating from Harvard Business School, Gomez has been pushing his opponent in the Senate race to release his taxes for the first time in his long political career.

Representative Edward J. Markey, the Democratic nominee, has said he will release his returns “in the very near future,” but has balked at committing to a date. A spokesman, Andrew Zucker, declined again Wednesday night to say whether the congressman would provide his tax returns Thursday.

“Congressman Ed Markey is a Washington insider who refuses to come clean with the voters of Massachusetts,” Gomez campaign spokesman Will Ritter
said in a statement. “Despite being paid by the taxpayers for the last 37 years, he still has yet to release a single year of tax returns. Gabriel Gomez has released his, what’s Congressman Ed Markey hiding?”

In contrast, Gomez opened the books to reveal his profits in the private sector. He made the bulk of his money with Advent International, the Boston-based firm he joined in 2004. Advent buys companies, makes changes to build them and cut costs, and tries to sell them at a profit.

In 2007, his most lucrative year at the firm, Gomez took home nearly $3 million, $2.3 million of that in capital gains, or profits from investments. His salary was a relatively small portion of his total compensation, at $418,438.

After several years trying his hand at doing deals, Gomez shifted gears to more of a marketing and portfolio service role, building relationships with bankers who bring investments to Advent, according to people affiliated with the firm. His earnings dropped by more than half from 2008, when he made $2,661,440, to $912,133 in 2009.

Gomez has not released his 2012 taxes; his campaign staff said he sought an extension and has not yet filed them.

However, a separate financial disclosure report that he was required to file as a candidate for the US Senate showed that he earned $993,470 at ­Advent last year.

That report, filed with the secretary of the US Senate, also shows that his largest holdings by far are in Advent funds and related investment vehicles. His holdings in entities called Sunley House, the funds Advent partners use to co-invest in the firm’s deals, are worth between $6 million and $30 million, accord­ing to the broad ranges that the disclosure form provides.

His total assets, listed on his disclosure sheet, are worth between $11.3 million and $47.7 million, the form shows.

That disclosure form also shows that Gomez received carried interest credits, or his portion of investment profits, as part of his separation agreement with Advent. He left the firm in February to pursue his campaign for the Senate.

Federal tax legislation that was passed this year raised the top tax rate for individuals to 39.6 percent, but left untouched the so-called “carried interest” tax loophole that taxes private equity gains at just 20 percent. President Obama is looking to eliminate that loophole.

Gomez’s campaign staff previously released a summary of his tax filings that showed he earned $8.5 million over a five-year period, between 2007 and 2011. The documents released Wednesday included his 2006 tax return as well, putting the sum for the entire six-year period over the $10 million mark.

Gomez did not release his tax return for 2005, a year in which he claimed a tax credit worth $281,500 for maintaining the façade of his historic home in Cohasset, as the Globe has previously reported. Gomez’s campaign aides said he had agreed to provide six years’ worth of tax returns, the duration of a Senate term.

However, the Globe was not allowed to make copies of Gomez’s tax returns. Campaign aides restricted two reporters to just over an hour to review hundreds of pages of documents.

Gomez’s 2011 tax return ­also lists a foreign tax credit worth $428 for investments outside the United States, ­apparently in St. Vincent and the Grenadines, the Caribbean islands where he met his wife when she was a Peace Corps volunteer and he was in the ­Navy.

According to the Internal Revenue Service website, the foreign tax credit is intended to prevent a taxpayer from paying a US and a foreign tax on ­income.

The form shows Gomez had gross foreign income of $13,398 that year. Ritter, the Gomez campaign spokesman, could not immediately give more details on the tax filings.

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